The present invention relates to surgical apparatus and methods. In particular, it relates to apparatus and methods for treatment of blockages in body passages, particularly for removal of atherosclerotic plaques from arteries via endarterectomy.
Atherosclerosis is a progressive disease of the cardiovascular system characterized by a buildup of plaques within a patient""s arteries, resulting in a stenosis (narrowing) or occlusion (blockage) of the arterial lumen. Atherosclerotic plaques are generally deposits of cholesterol and lipids within the intimal layer of the arteries, which may also become calcified over time. When the arterial lumen becomes too narrow, it can cause ischemia in the tissue and organs downstream of the blockage, resulting in pain (angina or claudication), dysfunction, necrosis and even death, depending on what organ systems are involved.
One of the common treatments for atherosclerosis is arterial bypass grafting, wherein an artificial or biological conduit or bypass graft is used to reroute blood flow around the blockage. This is a complex surgical procedure, sometimes involving considerable morbidity and a risk of eventual occlusion of the bypass graft as the underlying disease progresses. Other treatments include dilatation or angioplasty, in which a tapered dilator or a balloon catheter is used to push the plaque aside to open the arterial lumen, and atherectomy, which involves cutting and removal or comminution of the plaque material. Stenting is an adjunct to angioplasty and atherectomy in which a vascular endoprosthesis (a stent) is implanted in the artery to maintain an open lumen after dilating or debulking the lesion. These approaches are most effective for discrete, focal lesions and are less effective for long lesions and diffuse atherosclerotic disease. Clinical data also indicate that there is a significant percentage of restenosis after both angioplasty and atherectomy, even with stenting. Furthermore, angioplasty, atherectomy and stents are ineffective in arteries with total occlusions. However, because angioplasty and atherectomy can be performed using minimally invasive catheter techniques, these approaches are sometimes favored for treating lesions that are difficult to access surgically, for example in coronary artery disease.
For atherosclerotic lesions in arteries that are surgically accessible, particularly long or diffuse lesions, endarterectomy is considered to be a more definitive treatment than angioplasty or atherectomy and, with advanced techniques, offers lower morbidity than surgical bypass. Endarterectomy involves surgically opening the artery, removing plaque from the interior of the artery and surgically closing the artery. To remove plaque, a plane of separation is established between the plaque and the medial layer of the artery. The plaque is dissected away from the media along the plane of separation and removed, along with the endothelial layer of the artery. If the plaque is long and extends beyond the portion of the artery to be treated, the plane of separation is smoothly terminated on its proximal and distal ends to prevent further dissection of the arterial wall. Endarterectomy has the advantage that it preserves the original arterial conduit, maintaining the original flow geometry and topology and offering a hemocompatible arterial lining with proven long-term patency. Endarterectomy actually removes the plaque rather than simply pushing it aside or routing blood flow around it. In addition, endarterectomy can also be used to effectively treat totally occluded arteries.
As an adjunct, a stent or stent graft may be implanted to re-line the vessel after endarterectomy. Alternatively or in addition, stents may be used in the transition zones at the ends of the treated portion of the artery to prevent further dissection of the arterial wall. The stent or stent graft will prevent abrupt reclosure and may reduce the occurrence of restenosis in the long term. Other adjunctive treatments may be used to reduce the chance of intimal hyperplasia or long term restenosis. These treatments include radiation therapy (e.g. brachytherapy), therapeutic ultrasound, local or systemic drugs and gene therapy.
Standard open endarterectomy has a disadvantage in that a long incision is required to expose and open the entire length of the arterial section to be treated. In order to reduce the size of the incision needed, and the concomitant morbidity involved, methods have been devised for performing endarterectomy less invasively. These methods generally involve making a series of small incisions at intervals along the length of the artery and using elongated instruments to separate and remove the plaques from the arterial lumen between the incisions, while keeping the arteries relatively intact. Examples of instruments for facilitating less invasive endarterectomy can be found in U.S. Pat. No. 4,290,427 to Albert K. Chin and Thomas J. Fogarty and in U.S. Pat. No. 5,843,102 to Menno Kalmann and Franciscus Laurens Moll, which are hereby incorporated in their entirety. Less invasive or remote endarterectomy has the advantages of standard endarterectomy and the additional advantages that it produces less trauma and morbidity than either standard endarterectomy or bypass surgery and, with the appropriate techniques, can entirely avoid the difficulty of end-to-side or end-to-end anastomoses. Although less invasive endarterectomy has a great many advantages, the current instruments and methods have limitations in terms of the length of the artery that can be treated through a single incision. They are also limited in the amount of variation allowable in the arterial wall that can be treated. Variations in the arterial wall that can interfere with treatment can be caused by tortuosity of the arteries and by changes in diameter of the artery over its length, as well as other factors. These limitations are closely related, since the longer the section of the artery to be treated, the more likely it is to have such variations in the arterial wall.
While the prior endarterectomy apparatus and methods represent a significant step forward in the treatment of atherosclerosis, continued research has been directed toward further improvements in the technology for performing endarterectomy. In particular, research has been directed toward devising instruments and methods that facilitate performing endarterectomy over longer lengths of artery, through fewer and smaller incisions and, ideally, to allow dissection, termination and removal of atherosclerotic plaques over long lengths of artery through a single incision. In furtherance of this goal, this research has also been directed toward devising apparatus and methods that will facilitate effective endarterectomy despite variations in the arterial wall due to tortuosity or diameter changes.
In keeping with the foregoing discussion, the present invention takes the form of improved apparatus and methods for performing endarterectomy remotely via intraluminal techniques. The endarterectomy apparatus of the present invention takes the form of a flexible blade dissector having a flexible dissecting blade mounted at the distal end of an elongated catheter shaft. In a preferred embodiment, the flexible dissecting blade is approximately diamond shaped, having approximately triangular shaped lateral wings arranged symmetrically on the left and right side of the catheter shaft. The distal edge of the flexible dissecting blade is configured as a dissecting edge capable of initiating and extending a plane of dissection between an atheromatous plaque and the medial layer of the artery without cutting into either the plaque or the tissue of the medial layer. The distal edge of the flexible dissecting blade may be sharpened to form a sharp dissecting edge or, alternatively, it may be rounded to form a blunt dissecting edge. The flexible dissecting blade is constructed to have differential stiffness such that the lateral wings will readily bend around a central longitudinal axis, but will resist bending perpendicular to this axis. Stiffeners or other structures may be incorporated into the flexible dissecting blade to enhance the differential stiffness. Preferably, the flexible dissecting blade is made with an initial curve, which helps it to conform to the curvature of the arterial wall. The flexible blade dissector may incorporate a steering mechanism to direct the flexible dissecting blade along a preferred path within the arterial wall.
In one preferred embodiment, the apparatus includes a first flexible blade dissector and a second flexible blade dissector that slides coaxially over the catheter shaft of the first flexible blade dissector. The flexible dissecting blade of the second device is made wider than the dissecting blade of the first device in order to expand the plane of dissection laterally within the arterial wall.
The endarterectomy method of the present invention is practiced by making an incision into an artery wall and initiating a plane of separation between an atherosclerotic plaque and the medial layer of the artery wall, inserting the flexible blade dissector into the plane of separation and advancing the flexible dissecting blade to longitudinally extend the plane of separation. Optionally, a second flexible blade dissector may be inserted into the plane of separation coaxially over the catheter shaft of the first device and advanced to laterally expand the plane of separation. Once the plaque has been freed from the entire inner circumference of the arterial lumen, the plane of separation is terminated on the distal and proximal ends if necessary, and the plaque is removed from the arterial lumen, using known techniques.